Pianos are known that have an electronic sound source as well as the usual acoustic sound mechanism, and can be switched between an acoustic sound mode in which only acoustic sound is generated by hammer's striking the strings and an electronic sound mode in which only electronic sound is generated. In such pianos, the hammers are prohibited from striking the strings when the piano is in the electronic sound mode. The prohibition is performed by a stop rail which abuts and thereby stops the hammer shanks which move in response to the depression of corresponding keys of the piano.
Stop rail 90 shown in FIG. 5A is an example of the prior art. The stop rail 90 is rotatable between the stop position, indicated by solid lines, to stop the movement of the hammer shanks 100, only one of which is shown, and the retracted position, indicated by broken lines, to permit the hammer shanks 100 to continue moving until the not-shown hammers strike the not shown strings.
Stop rail 91 shown in FIG. 5B is another example of the prior art. The stop rail 91 is movable in pure translational movement in a direction perpendicular to the longitudinal axes of the hammer shanks 100, only one of which is shown, between the stop position (solid lines) and the retracted position (broken lines).
In order to effectively stop the hammer shanks 100, the stop rails must be located in the limited available space between the strings, the hammer shanks and the damping mechanism. Since the space where the silencing unit is installed is very narrow, it is not an easy task to install the stop rail. Moreover, if the stop rail is to travel in the manner shown in FIG. 5A, the stop rail may interfere with other components inside the piano. In view of the functions of the stop rail at the stop position and at the retracted position, the range of travel of the stop rail between the stop position to the retracted position is preferably made over the greatest possible distance. With the prior art stop rails, however, this leads to a greater width L of the stop rail, which requires a larger available space and increases the difficulty in installation. The arrangement shown in FIG. 5B also suffers from deficiencies in its relatively complicated travel mechanism and its uneasy adjustment, since pure translational movement is required to be more accurate than the rotational movement shown in FIG. 5A.
For example, if a stop rail of a greater size is adopted, it may intrude upon the pivoting range of the dampers or damper wires disposed along the strings, thereby spoiling the function of the damper unit. If the stop rail is arranged based only upon avoiding the affect on the damper unit, it may fail to effectively stop the hammer shanks before they strike the strings, or may touch the hammer shanks even when the acoustic sound is not to be silenced.